The present invention relates to an encapsulated endoscope.
It is generally known to provide a vertical scanning circuit for electronic shutter as a means for controlling exposure amount in solid-state imaging apparatus that are used in various imaging apparatus. The construction and method of controlling exposure amount will be described below of a prior-art solid-state imaging apparatus (area sensor) disclosed in Japanese Patent Application Laid-Open Hei-5-227489. FIG. 1 is a block diagram of an overall construction of area sensor 40 as disclosed in the above publication. The area sensor 40 includes: a pixel section 13 having a plurality of pixels two-dimensionally disposed in rows and columns; a vertical scanning circuit 15 (hereinafter referred to as read vertical scanning circuit) for selecting a row of the pixel signals of the pixel section 13 to be read and sequentially switching the selected row; a vertical scanning line 16 for connecting between the pixel section 13 and the read vertical scanning circuit 15; a vertical scanning circuit 42 (hereinafter referred to as electronic shutter vertical scanning circuit) for resetting charge signals accumulated at the pixels; a vertical scanning line 16′ for connecting between the pixel section 13 and the electronic shutter vertical scanning circuit 42; a vertical signal line 17 onto which the pixel signals of the rows to be read, selected at the read vertical scanning circuit 15 are outputted; a horizontal read circuit 14 for sequentially outputting the signals outputted onto the vertical signal line 17; and an operation control section 19 for controlling operation of the area sensor 40.
The pixel section 13 consists of a light-receiving pixel region 11 and a light-blocked pixel region 12. The read vertical scanning circuit 15 is provided to the left of the pixel section 13 while the electronic shutter vertical scanning circuit 42 is provided to the right of the pixel section 13.
FIG. 2 is a timing chart for explaining an exposure amount control operation when light is continuously irradiated onto the area sensor 40. Supposing that the scanning direction of the read vertical scanning circuit 15 and the electronic shutter vertical scanning circuit 42 of the area sensor 40 is from the upper portion to the lower portion of the pixel section 13, the signals accumulated at the pixels are reset once between n-th and (n+1)-th frames as shown in the timing chart of the reset signal output and pixel region output of FIG. 2, and pixel signals accumulated again after the resetting are read out. The exposure time (exposure time 1, exposure time 2) for thus read pixel signals is time from the resetting to the readout, i.e., the time difference between the reset timing of a-th row and the read timing of a-th row.
Such exposure time then is proportional to the number of rows occurring between the row (b-th row in the illustrated example) where pixel signals are being reset by the electronic shutter scanning circuit 42 at a point in time t1 when pixel signals (a-th row in the illustrated example) are read out by the read scanning circuit 15 and the row (a-th row) where the pixel signals are being read out by the read scanning circuit 15. The exposure time, therefore, is controlled by changing such number of rows.
In addition, of imaging apparatus for taking images of a dark part for example in the body cavity, there is a method of controlling exposure amount by controlling an emission of light source. FIG. 3 shows an encapsulated endoscope where such exposure amount control method is used as disclosed in Japanese Patent Application Laid-Open 2005-552.
As shown in FIG. 3, an encapsulated endoscope 2 disclosed in the above publication has an outward appearance of a capsule-type tablet form. It includes a case 3 for example of a resin formed into a capsule having a substantially oval longitudinal section. A front portion of case 3 is formed of a transparent member 3a. At the interior of the case 3, the encapsulated endoscope 2 has its main portion where the following members are disposed. In particular, disposed in a front portion facing the transparent member 3a are: a light source 6 for example of LED for illuminating an object to be taken such as a digestive organ within the body cavity; an observation optical system 8 (hereinafter referred to as objective lens) for forming an optical image of the object illuminated by the light source 6; and an area sensor 40 consisting for example of CCD or CMOS sensor for taking an image through the objective lens 8 and effecting predetermined photoelectric conversion processing to generate image signals. Disposed from there toward the back are: a light source drive control section 5 receiving output from the area sensor 40 for controlling light amount or light-emitting time of and driving the light source 6; a drive control/signal processing unit 9 having a drive control circuit and signal processing circuit of the area sensor 40; a communication unit 10 receiving image signals outputted from the drive control/signal processing unit 9 to transmit/output the same to a predetermined receiving/record ing apparatus (not shown) provided at the outside of the body cavity for example with using a wireless communication; and a power supply 4 consisting of power supply batteries 4a and 4b. 
Of thus constructed encapsulated endoscope 2, the light source drive control section 5 determines light emitting conditions (emitting light amount and/or emitting time) of the light source 6 based on the output signals of the area sensor 40 and drives the light source 6 based on the determined light emitting conditions using the drive signals from the drive control/signal processing unit 9.
FIG. 4 shows drive timing (timing of light source drive current) of the light source 6 and the drive timing (timing of pixel region output) of the area sensor 40. In a dark part such as in the body cavity, light does not enter the area sensor 40 unless the light source 6 is caused to emit. In other words, the emitting time of the light source 6 is the exposure time of the area sensor 40. Accordingly, the exposure amount of the area sensor 40 can be controlled by controlling the light emitting conditions of the light source 6.
In the case where MOS imaging device is mounted on an encapsulated endoscope and the exposure amount is controlled at the light source, an electronic shutter function provided at an ordinary MOS imaging device is unnecessary because the interior of the body cavity is dark. On the other hand, there is a limit on the length and/or thickness of an encapsulated endoscope, since the encapsulated endoscope is to take images at the interior of the body cavity. For this reason, size reduction of MOS imaging device is a necessity when downsizing of the encapsulated endoscope is considered.